The invention relates to an electrical system for road vehicles and specifically the relationship between the vehicle""s electrical system and drive-train for controlling torque, power generation, and engine start-up.
Commercial vehicles such as semi-trucks, garbage haulers, buses and the like, often incorporate a retarder as a way to reduce the vehicle""s velocity without having to utilize friction brakes every time the vehicle is required to slow. Use of a retarder would therefore be a way to extend the useful life of a vehicle""s brakes and avoid frequent and costly brake maintenance.
The power supply for these retarder devices can come from several sources. Some retarders operate by controlling the intake and exhaust valves of an engine; some by restricting engine exhaust; while other retarders are designed to utilize hydraulic power, magnetic or electromagnetic interaction. All retarders function to absorb or dissipate the kinetic energy associated with a moving vehicle.
In this specification, retardation is defined as the use of an electromagnetic retarder to slow a vehicle.
For electromagnetic retarders, two methods are known in the prior art for exciting its magnetic field:
One method uses the vehicle""s battery and alternator, as a power source. As illustrated in FIG. 2, retarder 30 competes with the rest of the vehicle loads for available power. During retardation, which occurs for example when traveling downhill, the engine is operating at a lower RPM. For this situation, the output of alternator 22 is insufficient to maintain the battery fully-charged. Also, retardation causes depletion of the battery charge.
The second method uses permanent magnets instead of a field winding. In this configuration, there is no demand placed upon the vehicle battery and alternator for retardation. However, the torque produced by retardation is limited primarily to either a full ON or full OFF condition. Alternatively, a costly rotor displacement mechanism can be incorporated which would provide the ability to vary the voltage.
The invention is best described as an electromagnetic retarder system for use with motorized vehicles. Additional functions can comprise the retarder system which can be adapted to include one or a combination of the following: 1) a brushless DC alternator; 2) a brushless DC starter; 3) a passive/active damper that replaces the vehicle""s flywheel; 4) a transmission-synchronizing inertia brake; and, 5) a booster to offset the lag associated with using a turbocharger.
The housing which contains the retarder system may be integrated with the engine or with the transmission. While the engine is operating, it produces torque on the drive shaft for powering the transmission. When required, the retarder produces retardation torque, or negative torque, to reduce the velocity of a vehicle.
The retarder system can be positioned either at the input or the output of the transmission. Positioning is determined by the desired application, as each location has its own advantages.
For example, a retarder system placed at the output of a transmission can be made small and lightweight by providing it with a high speed shaft. However, at this position, the retarder system could not be an effective starter or generator because it rotates only when the transmission is engaged by the clutch or other torque link.
Conversely, a retarder system located at the input of a transmission, while large, may take advantage of gear ratios obtained from downshifting, to produce an even greater torque. Also, when the retarder rotor assembly, which will be discussed in detail below, is positioned between the engine and transmission, its function as a generator is unimpaired, as rotation occurs as long as the engine is running. Finally, because the rotor assembly of the retarder system is coupled directly to the crankshaft, the device can be used as a starter. For these stated reasons, the retarder system is preferably positioned between engine and transmission. Also, for this configuration, it is preferred that the induction ring or retarder drum be adapted for a coolant to pass through so that it can be connected to the vehicle""s existing cooling system (i.e. radiator) for dissipating the heat generated during retardation.
The invention comprises an electromagnetic retarder connected along the drive-shaft to an exciter generator. A permanent magnet generator (PMG) can also be on the same shaft but is not directly connected to either the retarder or exciter generator. The rotors of both the exciter generator and PMG as well as the field winding of the retarder are coupled either to a cooperating shaft which is coupled to the main drive shaft, or the cooperating shaft is actually the main drive shaft. In addition, at least one rectifier is positioned between and hard-wired to the field winding and exciter rotor. In the preferred embodiment, the field winding, the rectifier and the rotors of the exciter and PMG are collectively referred to as the retarder rotor assembly.
Positioned about the rotor assembly is a housing which can be integrated with either the engine or transmission housing, or as a separate housing. This housing preferably comprises the induction ring, and the stators of the exciter generator and PMG. Therefore, the retarder, exciter generator and PMG each have relatively rotatable elements, the stationary retarder induction ring and stators of the exciter generator and PMG, and their respective rotatable elements, the field winding and exciter rotor and PM rotor which rotate when the drive train is operable.
The exciter generator allows for brushless operation, while the PMG is referred to as xe2x80x9cself-excitedxe2x80x9d because its rotor is coupled to the vehicle""s drive-shaft and will produce current so long as the drive-shaft is rotating.
The electromagnetic retarder operates by energization of the rotating field winding of the rotor assembly to interact with a stationary induction ring to produce torque, which, together with drive-shaft rotation, generates power. Therefore, both of the retarder elements, the field winding and the induction ring are in surrounding relation to the main drive shaft.
It is important to note that, although torque may exist between the field winding of the rotor assembly and the induction ring even at a standstill due to magnetic attraction, for torque to be produced according to the invention, there must exist relative motion between the PMG rotor and stator. In other words, the field winding requires energization by an electric current which is created as a result of the output produced by the PMG.
This allows the PMG to convert mechanical power to the electrical energy required to energize the exciter generator and ultimately the field winding of the rotor assembly. Since the PMG will produce electricity whenever the drive-shaft is rotating, it is necessary to use a regulator to regulate the level of current-reaching the exciter stator. Operation of the regulator would depend upon the type of external signal received. In addition, a power conditioning unit (PCU) is required to condition the alternating current (AC) produced by the PMG into direct current (DC).
The invention will operate equally as well if the induction ring is made to rotate, and the magnetic field is held stationary.
In addition to furnishing the electrical energy to power the exciter generator, the PMG can also be used for charging the vehicle""s battery; thus eliminating the need for an alternator.
Further, the power flow through the PCU is partially reversible so that the battery can be used to motorize the PMG; thus eliminating the need for a starter.
Also, the inertia produced by the rotor assembly can effectively replace the engine flywheel. Controlled pulsing of the retarder in opposition to engine positive torque pulsations can achieve active torque damping. It is also possible to use the PMG as a motor and controllably pulse it in opposition to the engine""s negative torque pulsations to achieve a similar result, but with a higher net positive torque resulting.
Finally, it becomes possible to use the PMG as a motor to provide positive torque to the drive train, when a power boost is required. This power boost would be beneficial to compensate for the lag commonly encountered with a turbocharged system. The duration and amplitude of the boost would be limited by the capacity and state of charge of the battery.
Although the invention uses standard electromagnetic principles, i.e. a field interacting with an armature, it further provides the advantage of self-excitation, while retaining the controllability associated with field windings. This is accomplished by using an exciter generator in combination with a PMG on the same shaft and preferably within the same housing.
The invention has thus far taught an electromagnetic retarder by itself and in combination with one or more of four other functions. However, the principles discussed herein can also be applied without using a retarder in combination.
For example, a PMG configured with its rotor coupled to the drive-shaft and its stator thereabout can generate sufficient current to serve as an alternative to an alternator. Also, the vehicle starter can be replaced by utilizing the PMG as a brushless starter when an angular rotary position indicator is provided and an inverter is used to direct current from the vehicle""s battery.
Additional configurations can be obtained by combining the different functions mentioned above.
The invention provides the following advantages over the prior art:
The retarder system is self-excited in that it requires no energy from the vehicle""s battery or alternator. The battery therefore, will not be drained during the retardation cycle. The electrical power required to excite the retarder is generated by a PMG which converts mechanical energy from the rotating drive-shaft, into usable electricity.
The retarder system can be adapted so that the PMG is utilized to furnish electricity to charge the vehicle""s battery as well as providing electricity for the retarder""s operation; thus eliminating the need for an alternator.
The retarder system can also be adapted so that the battery can supply power to the PMG in a xe2x80x9cstarting modexe2x80x9d via a start inverter; thus eliminating the need for a starter. Also, with the engine running, the PMG can be made to compensate for turbocharging xe2x80x9clagxe2x80x9d by boosting the system with motive power.
The retarder system can also be adapted for use as an active/passive damper. The inertia developed by the rotor acts as a passive damper which can replace the flywheel. The retarder system can also employ active damping. The advantage of active damping is that mechanical stresses can be reduced, and thereby extend the life of the transmission, differential, and other drive train components.
The retarder system can also be adapted to replace the inertia brake commonly used in transmissions to aid in synchronizing gears while downshifting. The inertia brake is often expensive and requires the addition to the transmission of an extra power take off (PTO), consisting of at least a pair of gears.
Improved fuel efficiency will result from a reduction in overall vehicular weight. The prior art starter, which is a parasitic load as soon as the engine is started, is eliminated. The energy which would have been wasted as a parasitic load, is now available for other load purposes.
The retarder system results in improved reliability because: a) the number of component parts is reduced, b) the life of the transmission and other drive line components is extended because of a smoothing out of torque pulsations by the active damper, and, c) battery life can be extended because controlled starts minimize current surges encountered with normal, brush-type starters. Power management reduces the magnitude of power drain and extends the life of the battery.